1. Field of the Invention
This invention relates to a tray device capable of being easily united to a sheet handling system such as a copying machine and a sheet post-processing apparatus, and more particularly, to a tray device incorporating compactly a mechanism for moving vertically a sheet supporting plane in parallel in accordance with the thickness of sheets fed from the sheet handling system.
2. Description of the Prior Art
Sheet handling systems such as a sheet post-processing apparatus and a sheet sorting device, which are generally united to an image forming apparatus such as a copying machine, printer and facsimile, are provided with a sheet tray for holding and stacking sheets thereon. The sheet tray of a large storage type capable of stacking a large number of sheets has a large mechanism for vertically moving a sheet supporting plane in accordance with the number of sheets stacked therein.
The mechanism for vertically moving the tray incorporated in the sheet post-processing apparatus as described in U.S. Pat. No. 3,385,340 is composed of a rack formed on a device frame, a pinion engaged with the rack, and a motor mounted on the tray. In this prior art device, by driving the motor to rotate the pinion, the tray is moved vertically while being guided by use of guiding rollers along a guiding rail fixed on the device frame. There have also been various tray devices employing a tray moving mechanism having lifting belts instead of the rack and pinion.
In the tray device of any type having the driving components including rack and guiding elements, the counterpart components of the driving mechanism should be fixedly formed in advance on a sheet handling system to which the tray device is united, and therefore, requires a large-sized subsidiary means for moving the tray vertically, resulting in a large overall size of the sheet handling system.
The tray in the conventional tray device of the type driven by a driving motor has been heavy, thus burdening the driving motor in the mechanism for vertically moving the tray with heavy weight. As a result, the high-power driving motor being large in size and weight must be used for moving the heavy tray. Consequently, the motor becomes difficult of incorporation into the tray device and entails a disadvantage such that it must be assembled within the sheet- handling system to which the tray device is united. As is obvious from the circumstances, the conventional tray device has been used exclusively for a specific sheet handling system, but cannot be attached additionally to another existing system without any mounting means.
An object of the present invention is to provide a tray device for stacking thereon one or more sheets fed from a sheet handling system such as a sheet post-processing apparatus, which has a sheet supporting plane capable of being effectively moved vertically in parallel in accordance with the thickness of sheets stacked thereon.
Another object of the present invention is to provide a tray device capable of being efficiently operated even by a low-power driving motor producing having small motion power for lifting only the sheet supporting plane.
Still another object of the present invention is to provide a tray device having a wide use easily applicable to various sheet handling systems.
To attain the objects described above, there is provided a tray device comprising a tray member movable vertically relative to a device frame, and a tray driving means incorporated within the device frame for vertically moving the tray member.
The device frame is fixedly or demountably united to the sheet handling system. The tray driving means comprises a stationary gear fixed on the device frame, a movable gear fixed on the tray member, a planet gear placed between the stationary gear and the movable gear, and a tray lifting means for vertically moving the tray member. The rotating shafts of the stationary, movable and planet gears are linked together by a rocking arm member rotatable on the rotating shaft of the stationary gear. The stationary and movable gears may be formed of a sector gear, respectively.
As the tray lifting means, an electric motor for rotating the planet gear may be used.
The motor is driven in accordance with the amount of sheets fed onto the tray member, thereby to rotate the planet gear relative to the stationary gear, with the result that the movable gear revolves vertically round the rotating shaft of the stationary gear, consequently to move vertically the tray member in parallel.
In place of the motor serving as the tray lifting means, there may be used a spring having such a spring constant that it expands or contracts in accordance with the weight of the sheets stacked on the tray member.
The tray driving means for vertically moving the tray member in parallel can be incorporated compactly within the device frame, consequently diminishing the size and weight thereof. Thus, the tray device of the invention can be driven with high efficiently even by using a low-power motor, and can exactly deal with and store the sheets. According to the invention, there is no call for mounting a driving mechanism for vertically moving the tray member onto the sheet handling system, and therefore, the tray device can be applied to various sheet handling systems of any type.
Other objects and features of the present invention will be hereinafter explained in detail with reference to the accompanying drawings.